Non-planar semiconductor device having group iii-v material active region with multi-dielectric gate stack

ABSTRACT

Non-planar semiconductor devices having group III-V material active regions with multi-dielectric gate stacks are described. For example, a semiconductor device includes a hetero-structure disposed above a substrate. The hetero-structure includes a three-dimensional group III-V material body with a channel region. A source and drain material region is disposed above the three-dimensional group III-V material body. A trench is disposed in the source and drain material region separating a source region from a drain region, and exposing at least a portion of the channel region. A gate stack is disposed in the trench and on the exposed portion of the channel region. The gate stack includes first and second dielectric layers and a gate electrode.

TECHNICAL FIELD

Embodiments of the invention are in the field of semiconductor devicesand, in particular, non-planar semiconductor devices having group III-Vmaterial active regions with multi-dielectric gate stacks.

BACKGROUND

For the past several decades, the scaling of features in integratedcircuits has been a driving force behind an ever-growing semiconductorindustry. Scaling to smaller and smaller features enables increaseddensities of functional units on the limited real estate ofsemiconductor chips. For example, shrinking transistor size allows forthe incorporation of an increased number of memory devices on a chip,lending to the fabrication of products with increased capacity. Thedrive for ever-more capacity, however, is not without issue. Thenecessity to optimize the performance of each device becomesincreasingly significant.

Semiconductor devices formed in epitaxially grown semiconductorhetero-structures, such as in group III-V material systems, offerexceptionally high carrier mobility in the transistor channels due tolow effective mass along with reduced impurity scattering. Such devicesprovide high drive current performance and appear promising for futurelow power, high speed logic applications. However, significantimprovements are still needed in the area of group III-V material-baseddevices.

Additionally, in the manufacture of integrated circuit devices,multi-gate transistors, such as tri-gate transistors, have become moreprevalent as device dimensions continue to scale down. Many differenttechniques have been attempted to reduce junction leakage of suchtransistors. However, significant improvements are still needed in thearea of junction leakage suppression.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a cross-sectional view of a non-planar semiconductordevice having group III-V material active region with asingle-dielectric gate stack.

FIG. 1B is a plot of C/A as a function of V_(G) for the device of FIG.1A over a spectrum of 100 kHz to 2 MHz.

FIG. 2 illustrates a cross-sectional view of a non-planar semiconductordevice having a group III-V material active region with amulti-dielectric gate stack, in accordance with an embodiment of thepresent invention.

FIG. 3 illustrates a cross-sectional view of another non-planarsemiconductor device having a group III-V material active region with amulti-dielectric gate stack, in accordance with another embodiment ofthe present invention.

FIG. 4 illustrates an angled view of a non-planar semiconductor devicehaving a group III-V material active region with a multi-dielectric gatestack, in accordance with an embodiment of the present invention.

FIG. 5A illustrates a three-dimensional cross-sectional view of ananowire-based semiconductor structure, in accordance with an embodimentof the present invention.

FIG. 5B illustrates a cross-sectional channel view of the nanowire-basedsemiconductor structure of FIG. 5A, as taken along the a-a′ axis, inaccordance with an embodiment of the present invention.

FIG. 5C illustrates a cross-sectional spacer view of the nanowire-basedsemiconductor structure of FIG. 5A, as taken along the b-b′ axis, inaccordance with an embodiment of the present invention.

FIGS. 6A-6E illustrate cross-sectional views representing variousoperations in a method of fabricating a non-planar semiconductor devicehaving a group III-V material active region with a multi-dielectric gatestack, in accordance with an embodiment of the present invention.

FIG. 7 illustrates a computing device in accordance with oneimplementation of the invention.

DESCRIPTION OF THE EMBODIMENTS

Non-planar semiconductor devices having group III-V material activeregions with multi-dielectric gate stacks are described. In thefollowing description, numerous specific details are set forth, such asspecific integration and material regimes, in order to provide athorough understanding of embodiments of the present invention. It willbe apparent to one skilled in the art that embodiments of the presentinvention may be practiced without these specific details. In otherinstances, well-known features, such as integrated circuit designlayouts, are not described in detail in order to not unnecessarilyobscure embodiments of the present invention. Furthermore, it is to beunderstood that the various embodiments shown in the Figures areillustrative representations and are not necessarily drawn to scale.

One or more embodiments described herein are directed to non-planarsemiconductor devices having group III-V material active regions withmulti-dielectric gate stacks. In particular, dual oxide/passivationfeatures for group III-V material non-planar transistors are described.Embodiments may cover approaches for fabricating devices having one ormore of a dual oxide, a III-V channel, low off-state leakage, and may beapplicable to transistors based on non-silicon channel configurations.

With respect to providing a context for one or more embodimentsdescribed herein, past architectures for related devices may include orinvoke a leakage path in a III-V material based transistor. The leakagepath may be below the gate electrode and through a larger band-gapbottom barrier since the larger band-gap material is in contact with ahigh-k gate dielectric and may not be compatible with such a dielectric.Such contact with a high-k gate dielectric may result in an largedensity of interface traps and allow for a conduction path outside ofthe gate control of the device, thereby limiting the off-state leakageof the III-V transistor. Such issues may be enhanced in non-planartransistor structures.

As an example of a conventional approach, FIG. 1A illustrates across-sectional view of a non-planar semiconductor device having groupIII-V material active region with a single-dielectric gate stack.Referring to FIG. 1A, a semiconductor device 100 includes ahetero-structure 104 disposed above a substrate 102. Thehetero-structure 104 includes a three-dimensional group III-V materialbody 106 with a channel region 108. A source and drain material region110 is disposed above the three-dimensional group III-V material body106. A trench 112 having is disposed in the source and drain materialregion 110, separating a source region 114 from a drain region 116, andexposing at least a portion of the channel region 108. A gate stack 118is disposed in the trench 112 and on the exposed portion of the channelregion 108. The gate stack 118 includes a high-k gate dielectric layer122 and a gate electrode 124. It is to be understood that the gate stack118 includes a portion below the channel region, labeled 118A in FIG.1A. The hetero-structure 104 further includes a top barrier layer 126and a bottom barrier layer 128. The trench 112 is further disposed inthe top barrier layer 126 and partially into bottom barrier layer 128.As such, the gate stack 118 may completely surround the channel region108, as depicted in FIG. 1A.

Referring again to FIG. 1A, the high-k gate dielectric layer 122 is incontact with a high band-gap bottom barrier layer 128 (e.g., InAlAs).Interface states 140 may thus be generated and result in an unwantedleakage path 142 from source 114 to drain 116. Such a leakage path 142may detrimentally increase the off-state leakage of the device 100.Furthermore, providing such a thin and high capacitance gate dielectricas a spacer also results in high parasitic capacitance and may result inslower transistor operation in circuits (e.g., poor RF performance). Asan example, FIG. 1B is a plot 150 of C/A as a function of V_(G) fordevice 100 over a spectrum of 100 kHz to 2 MHz. As shown in plot 150, ahigh Dit is observed for current state of the art devices.

In order to address the above issues, one or more embodiments describedherein are directed to approaches for, and the resulting devices,introducing a dual oxide/passivation layer into a non-planar III-Vsemiconductor device. Such a dual oxide/passivation layer may beincluded to reduce interface state generation below the transistorchannel. In one embodiment, and outer oxide layer has a low dielectricconstant so if it is thin, it can be used both in the gate stack or alsoas a spacer oxide. In an embodiment, inclusion of such a stack resultsin less Dit, reduces the parasitic drain off-state leakage, and lowersparasitic capacitance. Furthermore, improvements in mobility in thechannel may be realized because of reduced scattering.

In a first example, FIG. 2 illustrates a cross-sectional view of anon-planar semiconductor device having a group III-V material activeregion with a multi-dielectric gate stack, in accordance with anembodiment of the present invention.

Referring to FIG. 2, a semiconductor device 200 includes ahetero-structure 204 disposed above a substrate 202. Thehetero-structure 204 includes a three-dimensional group III-V materialbody 206 with a channel region 208. A source and drain material region210 is disposed above the three-dimensional group III-V material body206. A trench 212 having a width W1 is disposed in the source and drainmaterial region 210, separating a source region 214 from a drain region216, and exposing at least a portion of the channel region 208. A gatestack 218 is disposed in the trench 212 and on the exposed portion ofthe channel region 208.

The gate stack 218 includes a first dielectric layer 220 conformal withthe trench 212 and disposed on outer portions, but not an inner portion,of the channel region 208, as depicted in FIG. 2. A second, different,dielectric layer 222 is conformal with the first dielectric layer 220and is disposed on the inner portion of the channel region 208, as isalso depicted in FIG. 2. A gate electrode 224 is disposed on the seconddielectric layer 222. Although depicted as T-shaped, gate electrode 224may instead have the T-portions in order to reduce capacitance effects.In an embodiment, the first dielectric layer 220 has a thicknessapproximately in the range of 2-15 nanometers, and the second dielectriclayer 222 has a thickness approximately in the range of 0.5-3nanometers. In one such embodiment, the trench 212 has a width (W1)approximately in the range of 15-60 nanometers. It is to be understoodthat the gate stack 218 includes a portion below the channel region,labeled 218A in FIG. 2.

Referring again to FIG. 2, in an embodiment, the hetero-structure 204further includes a top barrier layer 226 disposed between the source anddrain material region 210 and the three-dimensional group III-V materialbody 206. The trench 212 is also disposed in the top barrier layer 226.In an embodiment, the hetero-structure 204 further includes a bottombarrier layer 228 disposed between the substrate 202 and thethree-dimensional group III-V material body 206. In one such embodiment,the trench 212 is also partially disposed in the bottom barrier layer228, completely exposing the channel region 208. In that embodiment, thegate stack 218 completely surrounds the channel region 208, as indicatedin FIG. 2.

In a second example, both dielectric layers may be included in a stackcovering all of the exposed channel. For example, FIG. 3 illustrates across-sectional view of another non-planar semiconductor device having agroup III-V material active region with a multi-dielectric gate stack,in accordance with another embodiment of the present invention.

Referring to FIG. 3, a semiconductor device 300 includes ahetero-structure 204 disposed above a substrate 202. Thehetero-structure 204 includes a three-dimensional group III-V materialbody 206 with a channel region 208. A source and drain material region210 is disposed above the three-dimensional group III-V material body206. A trench 312 having a width W2 is disposed in the source and drainmaterial region 210, separating a source region 214 from a drain region216, and exposing at least a portion of the channel region 208. A gatestack 318 is disposed in the trench 312 and on the exposed portion ofthe channel region 208. It is to be understood that the gate stack 318includes a portion below the channel region, labeled 318A in FIG. 3.

The gate stack 218 includes a first dielectric layer 220 conformal withthe trench 312 and disposed on the exposed portion of the channel region208. A second, different, dielectric layer 222 is conformal with anddisposed on the first dielectric layer 220, but not directly on thechannel region 208. A gate electrode 224 is disposed on the seconddielectric layer 222. Although depicted as T-shaped, gate electrode 224may instead have the T-portions in order to reduce capacitance effects.In an embodiment, the first dielectric layer 220 has a thicknessapproximately in the range of 0.3-2 nanometers, and the seconddielectric layer 222 has a thickness approximately in the range of 0.5-3nanometers. In one such embodiment, the trench 312 has a width (W2)approximately in the range of 5-25 nanometers.

Referring again to FIG. 2, in an embodiment, the hetero-structure 204further includes a top barrier layer 226 disposed between the source anddrain material region 210 and the three-dimensional group III-V materialbody 206. The trench 312 is also disposed in the top barrier layer 226.In an embodiment, the hetero-structure 204 further includes a bottombarrier layer 228 disposed between the substrate 202 and thethree-dimensional group III-V material body 206. In one such embodiment,the trench 312 is also partially disposed in the bottom barrier layer228, completely exposing the channel region 208. In that embodiment, thegate stack 318 completely surrounds the channel region 208, as indicatedin FIG. 3. It is also to be understood that like feature designations ofFIG. 3 may be as described in association with FIG. 2.

Referring to FIGS. 2 and 3, in an embodiment, the second dielectriclayer 222 has a higher dielectric constant than the first dielectriclayer 220. In one such embodiment, the second dielectric layer 222 has adielectric constant greater than approximately 8 and the firstdielectric layer 220 has a dielectric constant approximately in therange of 4-8. In another such embodiment, the second dielectric layer222 is composed of a material such as, but not limited to, tantalumsilicon oxide (TaSiO_(x)), aluminum oxide (AlO_(x), with a dielectricconstant of approximately 8), hafnium oxide (HfO₂, with a dielectricconstant greater than 8), zirconium oxide (ZrO₂, with a dielectricconstant greater than 8), and lanthanum oxide (La₂O₃, with a dielectricconstant greater than 8). The first dielectric layer is composed of amaterial such as, but not limited to, aluminum silicate (AlSiO_(x), witha dielectric constant of approximately 6, where varying the Si contentin the AlSiO_(x) can move the dielectric constant higher, e.g., up to7), silicon oxynitride (SiON, with a dielectric constant ofapproximately 5.5), silicon dioxide (SiO₂, with a dielectric constant ofapproximately 4) and silicon nitride (Si₃N₄, with a dielectric constantapproximately in the range of 6-7). In an embodiment, gate electrode 224is composed of a material such as, but not limited to, a metal nitride,a metal carbide, a metal silicide, hafnium, zirconium, titanium,tantalum, aluminum, ruthenium, palladium, platinum, cobalt or nickel.The gate electrode stack 218 may also include dielectric spacers, notdepicted.

Substrate 202 may be composed of a material suitable for semiconductordevice fabrication. In one embodiment, substrate 202 is a bulk substratecomposed of a single crystal of a material which may include, but is notlimited to, silicon, germanium, silicon-germanium or a III-V compoundsemiconductor material. In another embodiment, substrate 202 includes abulk layer with a top epitaxial layer. In a specific embodiment, thebulk layer is composed of a single crystal of a material which mayinclude, but is not limited to, silicon, germanium, silicon-germanium, aIII-V compound semiconductor material or quartz, while the top epitaxiallayer is composed of a single crystal layer which may include, but isnot limited to, silicon, germanium, silicon-germanium or a III-Vcompound semiconductor material. In another embodiment, substrate 202includes a top epitaxial layer on a middle insulator layer which isabove a lower bulk layer. The top epitaxial layer is composed of asingle crystal layer which may include, but is not limited to, silicon(e.g., to form a silicon-on-insulator (SOI) semiconductor substrate),germanium, silicon-germanium or a III-V compound semiconductor material.The insulator layer is composed of a material which may include, but isnot limited to, silicon dioxide, silicon nitride or silicon oxy-nitride.The lower bulk layer is composed of a single crystal which may include,but is not limited to, silicon, germanium, silicon-germanium, a III-Vcompound semiconductor material or quartz. Substrate 202 may furtherinclude dopant impurity atoms.

Hetero-structure 204 include a stack of one or more crystallinesemiconductor layers, such as a compositional buffer layer (not shown)with the bottom barrier layer 228 disposed thereon. The compositionalbuffer layer may be composed of a crystalline material suitable toprovide a specific lattice structure onto which a bottom barrier layermay be formed with negligible dislocations. For example, in accordancewith an embodiment of the present invention, the compositional bufferlayer is used to change, by a gradient of lattice constants, the exposedgrowth surface of semiconductor hetero-structure 204 from the latticestructure of substrate 202 to one that is more compatible for epitaxialgrowth of high quality, low defect layers thereon. In one embodiment,the compositional buffer layer acts to provide a more suitable latticeconstant for epitaxial growth instead of an incompatible latticeconstant of substrate 202. In an embodiment, substrate 202 is composedof single-crystal silicon and the compositional buffer layer grades to abottom barrier layer composed of a layer of InAlAs having a thickness ofapproximately 1 micron. In an alternative embodiment, the compositionalbuffer layer is omitted because the lattice constant of substrate 202 issuitable for the growth of a bottom barrier layer 228 for a quantum-wellsemiconductor device.

The bottom barrier layer 228 may be composed of a material suitable toconfine a wave-function in a quantum-well formed thereon. In accordancewith an embodiment of the present invention, the bottom barrier layer228 has a lattice constant suitably matched to the top lattice constantof the compositional buffer layer, e.g., the lattice constants aresimilar enough that dislocation formation in the bottom barrier layer228 is negligible. In one embodiment, the bottom barrier layer 228 iscomposed of a layer of approximately In_(0.65)Al_(0.35)As having athickness of approximately 10 nanometers. In a specific embodiment, thebottom barrier layer 228 composed of the layer of approximatelyIn_(0.65)Al_(0.35)As is used for quantum confinement in an N-typesemiconductor device. In another embodiment, the bottom barrier layer228 is composed of a layer of approximately In_(0.65)Al_(0.35)Sb havinga thickness of approximately 10 nanometers. In a specific embodiment,the bottom barrier layer 228 composed of the layer of approximatelyIn_(0.65)Al₀₃₅Sb is used for quantum confinement in a P-typesemiconductor device.

The three-dimensional group III-V material body 206 may be composed of amaterial suitable to propagate a wave-function with low resistance. Inaccordance with an embodiment of the present invention,three-dimensional group III-V material body 206 has a lattice constantsuitably matched to the lattice constant of the bottom barrier layer 228of hetero-structure 204, e.g., the lattice constants are similar enoughthat dislocation formation in three-dimensional group III-V materialbody 206 is negligible. In an embodiment, three-dimensional group III-Vmaterial body 206 is composed of groups III (e.g. boron, aluminum,gallium or indium) and V (e.g. nitrogen, phosphorous, arsenic orantimony) elements. In one embodiment, three-dimensional group III-Vmaterial body 206 is composed of InAs or InSb. The three-dimensionalgroup III-V material body 206 may have a thickness suitable to propagatea substantial portion of a wave-function, e.g. suitable to inhibit asignificant portion of the wave-function from entering the bottombarrier layer 228 of hetero-structure 204 or a top barrier layer (e.g.,barrier layer 226) formed on three-dimensional group III-V material body206. In an embodiment, three-dimensional group III-V material body 206has a thickness (height) approximately in the range of 50-100 Angstroms.The width (dimension taken into the page as shown) may haveapproximately the same dimension, providing a three-dimensionalwire-type feature.

Top barrier layer 226 may be composed of a material suitable to confinea wave-function in a III-V material body/channel region formed thereunder. In accordance with an embodiment of the present invention, topbarrier layer 226 has a lattice constant suitably matched to the latticeconstant of channel region 206, e.g., the lattice constants are similarenough that dislocation formation in top barrier layer 226 isnegligible. In one embodiment, top barrier layer 226 is composed of alayer of material such as, but not limited to, N-type InGaAs. Source anddrain material region 210 may be doped group III-V material region, sucha more heavily doped structure formed from the same or similar materialas top barrier layer 226. In other embodiments, the composition ofsource and drain material region 210, aside from doping differences,differs from the material of top barrier layer 226.

Semiconductor device 200 or 300 may be a semiconductor deviceincorporating a gate, a channel region and a pair of source/drainregions. In an embodiment, semiconductor device 200 or 300 is one suchas, but not limited to, a MOS-FET or a Microelectromechanical System(MEMS). In one embodiment, semiconductor device 200 or 300 is a planaror three-dimensional MOS-FET and is an isolated device or is one devicein a plurality of nested devices. As will be appreciated for a typicalintegrated circuit, both N- and P-channel transistors may be fabricatedon a single substrate to form a CMOS integrated circuit. Furthermore,additional interconnect wiring may be fabricated in order to integratesuch devices into an integrated circuit.

The above described devices can be viewed as trench-based devices, wherea gate wraps a channel region within a trench of a stack of III-Vmaterial layers. However, other devices may include a protruding III-Vchannel regions, such as in a tri-gate or FIN-FET based MOS-FETs. Forexample, FIG. 4 illustrates an angled view of a non-planar semiconductordevice having a group III-V material active region with amulti-dielectric gate stack, in accordance with an embodiment of thepresent invention.

Referring to FIG. 4, a semiconductor device 400 includes ahetero-structure 404 disposed above a substrate 202. Thehetero-structure 404 includes a bottom barrier layer 228. Athree-dimensional group III-V material body 206 with a channel region208 is disposed above the bottom barrier layer 228. A gate stack 218 isdisposed to surround at least a portion of the channel region 208. In anembodiment, not viewable from the perspective of FIG. 4, the gate stackcompletely surrounds the channel region 208. The gate stack 218 includesa gate electrode 224 and a dual gate dielectric layer 220/222, such asthe dual date dielectric layers described in association with FIGS. 2and 3. The gate stack may further include dielectric spacers 460.

Source and drain regions 414/416 may be formed in or on portions of thethree-dimensional group III-V material body 206 not surrounded by gatestack 218. Furthermore, a top barrier layer may be included in thoseregions as well. Also, isolation regions 470 may be included. Althoughdepicted in FIG. 4 as being somewhat aligned with the bottom of thebottom barrier layer 228, it is to be understood that the depth of theisolation regions 470 may vary. Also, although depicted in FIG. 4 asbeing somewhat aligned with the top of the bottom barrier layer 228, itis to be understood that the height of the isolation regions 470 mayvary. It is also to be understood that like feature designations of FIG.4 may be as described in association with FIG. 2.

In another aspect, FIG. 5A illustrates a three-dimensionalcross-sectional view of a group III-V material nanowire-basedsemiconductor structure, in accordance with an embodiment of the presentinvention. FIG. 5B illustrates a cross-sectional channel view of thegroup III-V material nanowire-based semiconductor structure of FIG. 5A,as taken along the a-a′ axis. FIG. 5C illustrates a cross-sectionalspacer view of the group III-V material nanowire-based semiconductorstructure of FIG. 5A, as taken along the b-b′ axis.

Referring to FIG. 5A, a semiconductor device 500 includes one or morevertically stacked group III-V material nanowires (550 set) disposedabove a substrate 202. Embodiments herein are targeted at both singlewire devices and multiple wire devices. As an example, a threenanowire-based devices having nanowires 550A, 550B and 550C is shown forillustrative purposes. For convenience of description, nanowire 550A isused as an example where description is focused on only one of thenanowires. It is to be understood that where attributes of one nanowireare described, embodiments based on a plurality of nanowires may havethe same attributes for each of the nanowires.

At least the first nanowire 550A includes a group III-V material channelregion 208. The group III-V material channel region 208 has a length(L). Referring to FIG. 5B, the group III-V material channel region 208also has a perimeter orthogonal to the length (L). Referring to bothFIGS. 5A and 5B, a gate electrode stack 218 surrounds the entireperimeter of each of the channel regions of each nanowire 550, includinggroup III-V material channel region 208. The gate electrode stack 218includes a gate electrode along with a gate dielectric layer disposedbetween the channel regions and the gate electrode (not individuallyshown). The group III-V material channel region 208 and the channelregions of the additional nanowires 550B and 550C are discrete in thatthey are completely surrounded by the gate electrode stack 218 withoutany intervening material such as underlying substrate material oroverlying channel fabrication materials. Accordingly, in embodimentshaving a plurality of nanowires 550, the channel regions of thenanowires are also discrete relative to one another, as depicted in FIG.5B. Referring to FIGS. 5A-5C, a bottom barrier layer 228 is disposedabove substrate 202. The bottom barrier layer 228 is further disposedbelow the one or more nanowires 550. In an embodiment, the group III-Vmaterial channel region 208 is completely surrounded by gate electrode218, as depicted in FIG. 5B.

Referring again to FIG. 5A, each of the nanowires 550 also includessource and drain regions 214 and 216 disposed in or on the nanowire oneither side of the channel regions, including on either side of groupIII-V material channel region 208. In an embodiment, the source anddrain regions 214/216 are embedded source and drain regions, e.g., atleast a portion of the nanowires is removed and replaced with asource/drain material region. However, in another embodiment, the sourceand drain regions 214/216 are composed of, or at least include, portionsof the one or more nanowires 550.

A pair of contacts 570 is disposed over the source/drain regions214/216. In an embodiment, the semiconductor device 500 further includesa pair of spacers 540. The spacers 540 are disposed between the gateelectrode stack 218 and the pair of contacts 570. As described above,the channel regions and the source/drain regions are, in at leastseveral embodiments, made to be discrete. However, not all regions ofthe nanowires 550 need be, or even can be made to be discrete. Forexample, referring to FIG. 5C, nanowires 550A-550C are not discrete atthe location under spacers 540. In one embodiment, the stack ofnanowires 550A-550C have intervening semiconductor material 580 therebetween. In one embodiment, the bottom nanowire 550A is still in contactwith a portion of the bottom buffer layer 228, which is otherwiserecessed for gate stack 218 formation (FIG. 5B). Thus, in an embodiment,a portion of the plurality of vertically stacked nanowires 550 under oneor both of the spacers 540 is non-discrete.

It is to be understood that like feature designations of FIG. 5A-5C maybe as described in association with FIG. 2. Also, although the device500 described above is for a single device, a CMOS architecture may alsobe formed to include both NMOS and PMOS nanowire-based devices disposedon or above the same substrate. In an embodiment, the nanowires 550 maybe sized as wires or ribbons, and may have squared-off or roundedcorners.

In an embodiment, gate stack 218 is formed in a wide trench formedaround nanowires 550. In one such embodiment, the gate stack includes afirst dielectric layer disposed on outer portions, but not an innerportion, of each of the channel regions. A second, different, dielectriclayer is conformal with the first dielectric layer and disposed on theinner portion of each of the channel regions. A gate electrode isdisposed on the second dielectric layer. In a specific such embodiment,the first dielectric layer has a thickness approximately in the range of2-15 nanometers, and the second dielectric layer has a thicknessapproximately in the range of 0.5-3 nanometers.

In another embodiment, gate stack 218 is formed in a narrow trenchformed around nanowires 550. In one such embodiment, the gate stackincludes a first dielectric layer disposed on each of the channelregions. A second, different, dielectric layer is conformal with thefirst dielectric layer and is disposed on the first dielectric layer,but not on each of the channel regions. A gate electrode is disposed onthe second dielectric layer. In a specific such embodiment, the firstdielectric layer has a thickness approximately in the range of 0.3-2nanometers, and the second dielectric layer has a thicknessapproximately in the range of 0.5-3 nanometers.

In another aspect, methods of fabricating a group III-V material-basedsemiconductor structure are provided. For example, FIGS. 6A-6Eillustrate cross-sectional views representing various operations in amethod of fabricating a non-planar semiconductor device having a groupIII-V material active region with a multi-dielectric gate stack, inaccordance with an embodiment of the present invention. It is also to beunderstood that like feature designations of FIGS. 6A-6E may be asdescribed in association with FIGS. 2 and 3.

Referring to FIG. 6A, a bottom barrier layer 228 is formed above asubstrate 202. A III-V material layer is then formed on bottom barrierlayer 228 and patterned to form three-dimensional material body 206 withchannel region 208. Alternatively, the III-V material layer may beformed after or during the trench formation described in associationwith FIG. 6C.

Referring to FIG. 6B, a hetero-structure 690, which may include a topbarrier layer 226 and source and drain material region 210, is formedabove the three-dimensional material body 206 (or above the III-Vmaterial layer, if not yet patterned).

Referring to FIG. 6C, a trench 612 is formed in hetero-structure 690 andpartially into bottom barrier layer 228, exposing channel region 208. Inan embodiment, trench 612 is formed by a dry or wet etch process.

Referring to FIG. 6D, a dual dielectric stack 220/222 is formed intrench 612 and surrounding channel region 208. Then, referring to FIG.6E, a gate electrode 224 is formed on the dual dielectric stack 220/222.

Referring again to FIG. 6E, the trench 612 may be formed as a relativelywide trench or a relatively narrow trench, as was described inassociation with FIGS. s2 and 3. The process flow depicted in FIGS.6A-6E generally represents fabrication of a narrow trench and a specificdual dielectric stack formed therein. In another embodiment, a widetrench may be formed and then completely filled with a first dielectriclayer of the dual gate stack. The first dielectric layer may then bepatterned and a second dielectric layer formed thereon.

Thus, one or more embodiments described herein are targeted at III-Vmaterial active region arrangements integrated with dual gate dielectricstacks. Although described above with respect to benefits for non-planarand gate-all-around devices, benefits may also be achieved for planardevices without gate wrap-around features. Thus, such arrangements maybe included to form III-V material-based transistors such as planardevices, fin or tri-gate based devices, and gate all around devices,including nanowire-based devices. Embodiments described herein may beeffective for junction isolation in metal-oxide-semiconductor fieldeffect transistors (MOSFETs). It is to be understood that formation ofmaterials such as the III-V material layers described herein may beperformed by techniques such as, but not limited to, chemical vapordeposition (CVD) or molecular beam epitaxy (MBE), or other likeprocesses.

FIG. 7 illustrates a computing device 700 in accordance with oneimplementation of the invention. The computing device 700 houses a board702. The board 702 may include a number of components, including but notlimited to a processor 704 and at least one communication chip 706. Theprocessor 704 is physically and electrically coupled to the board 702.In some implementations the at least one communication chip 706 is alsophysically and electrically coupled to the board 702. In furtherimplementations, the communication chip 706 is part of the processor704.

Depending on its applications, computing device 700 may include othercomponents that may or may not be physically and electrically coupled tothe board 702. These other components include, but are not limited to,volatile memory (e.g., DRAM), non-volatile memory (e.g., ROM), flashmemory, a graphics processor, a digital signal processor, a cryptoprocessor, a chipset, an antenna, a display, a touchscreen display, atouchscreen controller, a battery, an audio codec, a video codec, apower amplifier, a global positioning system (GPS) device, a compass, anaccelerometer, a gyroscope, a speaker, a camera, and a mass storagedevice (such as hard disk drive, compact disk (CD), digital versatiledisk (DVD), and so forth).

The communication chip 706 enables wireless communications for thetransfer of data to and from the computing device 700. The term“wireless” and its derivatives may be used to describe circuits,devices, systems, methods, techniques, communications channels, etc.,that may communicate data through the use of modulated electromagneticradiation through a non-solid medium. The term does not imply that theassociated devices do not contain any wires, although in someembodiments they might not. The communication chip 706 may implement anyof a number of wireless standards or protocols, including but notlimited to Wi-Fi (IEEE 802.11 family), WiMAX (IEEE 802.16 family), IEEE802.20, long term evolution (LTE), Ev-DO, HSPA+, HSDPA+, HSUPA+, EDGE,GSM, GPRS, CDMA, TDMA, DECT, Bluetooth, derivatives thereof, as well asany other wireless protocols that are designated as 3G, 4G, 5G, andbeyond. The computing device 700 may include a plurality ofcommunication chips 706. For instance, a first communication chip 706may be dedicated to shorter range wireless communications such as Wi-Fiand Bluetooth and a second communication chip 706 may be dedicated tolonger range wireless communications such as GPS, EDGE, GPRS, CDMA,WiMAX, LTE, Ev-DO, and others.

The processor 704 of the computing device 700 includes an integratedcircuit die packaged within the processor 704. In some implementationsof the invention, the integrated circuit die of the processor includesone or more devices, such as MOS-FET transistors built in accordancewith implementations of the invention. The term “processor” may refer toany device or portion of a device that processes electronic data fromregisters and/or memory to transform that electronic data into otherelectronic data that may be stored in registers and/or memory.

The communication chip 706 also includes an integrated circuit diepackaged within the communication chip 706. In accordance with anotherimplementation of the invention, the integrated circuit die of thecommunication chip includes one or more devices, such as MOS-FETtransistors built in accordance with implementations of the invention.

In further implementations, another component housed within thecomputing device 700 may contain an integrated circuit die that includesone or more devices, such as MOS-FET transistors built in accordancewith implementations of the invention.

In various implementations, the computing device 700 may be a laptop, anetbook, a notebook, an ultrabook, a smartphone, a tablet, a personaldigital assistant (PDA), an ultra mobile PC, a mobile phone, a desktopcomputer, a server, a printer, a scanner, a monitor, a set-top box, anentertainment control unit, a digital camera, a portable music player,or a digital video recorder. In further implementations, the computingdevice 700 may be any other electronic device that processes data.

Thus, embodiments of the present invention include non-planarsemiconductor devices having group III-V material active regions withmulti-dielectric gate stacks.

In an embodiment, a semiconductor device includes a hetero-structuredisposed above a substrate. The hetero-structure includes athree-dimensional group III-V material body with a channel region. Asource and drain material region is disposed above the three-dimensionalgroup III-V material body. A trench is disposed in the source and drainmaterial region separating a source region from a drain region, andexposing at least a portion of the channel region. A gate stack isdisposed in the trench and on the exposed portion of the channel region.The gate stack includes a first dielectric layer conformal with thetrench and disposed on outer portions, but not an inner portion, of thechannel region. A second, different, dielectric layer is conformal withthe first dielectric layer and is disposed on the inner portion of thechannel region. A gate electrode is disposed on the second dielectriclayer.

In one embodiment, the second dielectric layer has a higher dielectricconstant than the first dielectric layer.

In one embodiment, the second dielectric layer has a dielectric constantgreater than approximately 8 and the first dielectric layer has adielectric constant approximately in the range of 4-8.

In one embodiment, the second dielectric layer is composed of a materialsuch as, but not limited to, tantalum silicon oxide (TaSiO_(x)),aluminum oxide (AlO_(x)), hafnium oxide (HfO₂), zirconium oxide (ZrO₂),or lanthanum oxide (La₂O₃), and the first dielectric layer is composedof a material such as, but not limited to, aluminum silicate(AlSiO_(x)), silicon oxynitride (SiON), silicon dioxide (SiO₂) orsilicon nitride (Si₃N₄).

In one embodiment, the first dielectric layer has a thicknessapproximately in the range of 2-15 nanometers, and the second dielectriclayer has a thickness approximately in the range of 0.5-3 nanometers.

In one embodiment, the hetero-structure further includes a top barrierlayer disposed between the source and drain material region and thethree-dimensional group III-V material body. The trench is also disposedin the top barrier layer.

In one embodiment, the hetero-structure further includes a bottombarrier layer disposed between the substrate and the three-dimensionalgroup III-V material body.

In one embodiment, the trench is also partially disposed in the bottombarrier layer, completely exposing the channel region. The gate stackcompletely surrounds the channel region.

In an embodiment, a semiconductor device includes a vertical arrangementof a plurality of group III-V material nanowires disposed above asubstrate. A gate stack is disposed on and completely surrounds channelregions of each of the group III-V material nanowires. The gate stackincludes a first dielectric layer disposed on outer portions, but not aninner portion, of each of the channel regions. A second, different,dielectric layer is conformal with the first dielectric layer anddisposed on the inner portion of each of the channel regions. A gateelectrode is disposed on the second dielectric layer. Source and drainregions surround portions of each of the group III-V material nanowires,on either side of the gate stack.

In one embodiment, the semiconductor structure further includes a topbarrier layer disposed between the source and drain regions and each ofthe group III-V material nanowires.

In one embodiment, the semiconductor structure further includes a bottombarrier layer disposed between the substrate and the bottom-most groupIII-V material nanowire. A bottom portion of the gate stack is disposedon the bottom barrier layer.

In one embodiment, the second dielectric layer has a higher dielectricconstant than the first dielectric layer.

In one embodiment, the second dielectric layer has a dielectric constantgreater than approximately 8 and the first dielectric layer has adielectric constant approximately in the range of 4-8.

In one embodiment, the second dielectric layer is composed of a materialsuch as, but not limited to, tantalum silicon oxide (TaSiO_(x)),aluminum oxide (AlO_(x)), hafnium oxide (HfO₂), zirconium oxide (ZrO₂),or lanthanum oxide (La₂O₃), and the first dielectric layer is composedof a material such as, but not limited to, aluminum silicate(AlSiO_(x)), silicon oxynitride (SiON), silicon dioxide (SiO₂) orsilicon nitride (Si₃N₄).

In one embodiment, the first dielectric layer has a thicknessapproximately in the range of 2-15 nanometers, and the second dielectriclayer has a thickness approximately in the range of 0.5-3 nanometers.

In an embodiment, a semiconductor device includes a hetero-structuredisposed above a substrate. The hetero-structure includes athree-dimensional group III-V material body with a channel region. Asource and drain material region is disposed above the three-dimensionalgroup III-V material body. A trench is disposed in the source and drainmaterial region separating a source region from a drain region, andexposing at least a portion of the channel region. A gate stack isdisposed in the trench and on the exposed portion of the channel region.The gate stack includes a first dielectric layer conformal with thetrench and disposed on the exposed portion of the channel region. Asecond, different, dielectric layer is conformal with and disposed onthe first dielectric layer, but not on the channel region. A gateelectrode is disposed on the second dielectric layer.

In one embodiment, the second dielectric layer has a higher dielectricconstant than the first dielectric layer.

In one embodiment, the second dielectric layer has a dielectric constantgreater than approximately 8 and the first dielectric layer has adielectric constant approximately in the range of 4-8.

In one embodiment, the second dielectric layer is composed of a materialsuch as, but not limited to, tantalum silicon oxide (TaSiO_(x)),aluminum oxide (AlO_(x)), hafnium oxide (HfO₂), zirconium oxide (ZrO₂),or lanthanum oxide (La₂O₃), and the first dielectric layer is composedof a material such as, but not limited to, aluminum silicate(AlSiO_(x)), silicon oxynitride (SiON), silicon dioxide (SiO₂) orsilicon nitride (Si₃N₄).

In one embodiment, the first dielectric layer has a thicknessapproximately in the range of 0.3-2 nanometers, and the seconddielectric layer has a thickness approximately in the range of 0.5-3nanometers.

In one embodiment, the hetero-structure further includes a top barrierlayer disposed between the source and drain material region and thethree-dimensional group III-V material body. The trench is also disposedin the top barrier layer.

In one embodiment, the hetero-structure further includes a bottombarrier layer disposed between the substrate and the three-dimensionalgroup III-V material body.

In one embodiment, the trench is also partially disposed in the bottombarrier layer, completely exposing the channel region. The gate stackcompletely surrounds the channel region.

In an embodiment, a semiconductor device includes a vertical arrangementof a plurality of group III-V material nanowires disposed above asubstrate. A gate stack is disposed on and completely surrounds channelregions of each of the group III-V material nanowires. The gate stackincludes a first dielectric layer disposed on each of the channelregions. A second, different, dielectric layer is conformal with thefirst dielectric layer and is disposed on the first dielectric layer,but not on each of the channel regions. A gate electrode is disposed onthe second dielectric layer. Source and drain regions surround portionsof each of the group III-V material nanowires, on either side of thegate stack.

In one embodiment, the semiconductor structure further includes a topbarrier layer disposed between the source and drain regions and each ofthe group III-V material nanowires.

In one embodiment, the semiconductor structure further includes a bottombarrier layer disposed between the substrate and the bottom-most groupIII-V material nanowire. A bottom portion of the gate stack is disposedon the bottom barrier layer.

In one embodiment, the second dielectric layer has a higher dielectricconstant than the first dielectric layer.

In one embodiment, the second dielectric layer has a dielectric constantgreater than approximately 8 and the first dielectric layer has adielectric constant approximately in the range of 4-8.

In one embodiment, the second dielectric layer is composed of a materialsuch as, but not limited to, tantalum silicon oxide (TaSiO_(x)),aluminum oxide (AlO_(x)), hafnium oxide (HfO₂), zirconium oxide (ZrO₂),or lanthanum oxide (La₂O₃), and the first dielectric layer is composedof a material such as, but not limited to, aluminum silicate(AlSiO_(x)), silicon oxynitride (SiON), silicon dioxide (SiO₂) orsilicon nitride (Si₃N₄).

In one embodiment, the first dielectric layer has a thicknessapproximately in the range of 0.3-2 nanometers, and the seconddielectric layer has a thickness approximately in the range of 0.5-3nanometers.

1. A semiconductor device, comprising: a hetero-structure disposed abovea substrate and comprising a three-dimensional group III-V material bodywith a channel region, and further comprising a bottom barrier layerdisposed between the substrate and the three-dimensional group III-Vmaterial body; a source and drain material region disposed above thethree-dimensional group III-V material body; a trench disposed in thesource and drain material region separating a source region from a drainregion, the trench also partially disposed in the bottom barrier layerand completely exposing the channel region; and a gate stack disposed inthe trench and on and completely surrounding the channel region, thegate stack comprising: a first dielectric layer conformal with thetrench and disposed on outer portions, but not an inner portion, of thechannel region; a second, different, dielectric layer conformal with thefirst dielectric layer and disposed on the inner portion of the channelregion; and a gate electrode disposed on the second dielectric layer. 2.The semiconductor device of claim 1, wherein the second dielectric layerhas a higher dielectric constant than the first dielectric layer.
 3. Thesemiconductor device of claim 2, wherein the second dielectric layer hasa dielectric constant greater than approximately 8 and the firstdielectric layer has a dielectric constant approximately in the range of4-8.
 4. The semiconductor device of claim 2, wherein the seconddielectric layer comprises a material selected from the group consistingof tantalum silicon oxide (TaSiO_(x)), aluminum oxide (AlO_(x)), hafniumoxide (HfO₂), zirconium oxide (ZrO₂), and lanthanum oxide (La₂O₃), andthe first dielectric layer comprises a material selected from the groupconsisting of aluminum silicate (AlSiO_(x)), silicon oxynitride (SiON),silicon dioxide (SiO₂) and silicon nitride (Si₃N₄).
 5. The semiconductorstructure of claim 1, wherein the first dielectric layer has a thicknessapproximately in the range of 2-15 nanometers, and the second dielectriclayer has a thickness approximately in the range of 0.5-3 nanometers. 6.The semiconductor structure of claim 1, the hetero-structure furthercomprising: a top barrier layer disposed between the source and drainmaterial region and the three-dimensional group III-V material body,wherein the trench is also disposed in the top barrier layer. 7-8.(canceled)
 9. A semiconductor device, comprising: a vertical arrangementof a plurality of group III-V material nanowires disposed above asubstrate; a gate stack disposed on and completely surrounding channelregions of each of the group III-V material nanowires, the gate stackcomprising: a first dielectric layer disposed on outer portions, but notan inner portion, of each of the channel regions; a second, different,dielectric layer conformal with the first dielectric layer and disposedon the inner portion of each of the channel regions; and a gateelectrode disposed on the second dielectric layer; a bottom barrierlayer disposed between the substrate and the bottom-most group III-Vmaterial nanowire, wherein a bottom portion of the gate stack isdisposed on the bottom barrier layer; and source and drain regionssurrounding portions of each of the group III-V material nanowires, oneither side of the gate stack.
 10. The semiconductor structure of claim9, further comprising: a top barrier layer disposed between the sourceand drain regions and each of the group III-V material nanowires. 11.(canceled)
 12. The semiconductor device of claim 9, wherein the seconddielectric layer has a higher dielectric constant than the firstdielectric layer.
 13. The semiconductor device of claim 12, wherein thesecond dielectric layer has a dielectric constant greater thanapproximately 8 and the first dielectric layer has a dielectric constantapproximately in the range of 4-8.
 14. The semiconductor device of claim12, wherein the second dielectric layer comprises a material selectedfrom the group consisting of tantalum silicon oxide (TaSiO_(x)),aluminum oxide (AlO_(x)), hafnium oxide (HfO₂), zirconium oxide (ZrO₂),and lanthanum oxide (La₂O₃), and the first dielectric layer comprises amaterial selected from the group consisting of aluminum silicate(AlSiO_(x)), silicon oxynitride (SiON), silicon dioxide (SiO₂) andsilicon nitride (Si₃N₄).
 15. The semiconductor structure of claim 9,wherein the first dielectric layer has a thickness approximately in therange of 2-15 nanometers, and the second dielectric layer has athickness approximately in the range of 0.5-3 nanometers.
 16. Asemiconductor device, comprising: a hetero-structure disposed above asubstrate and comprising a three-dimensional group III-V material bodywith a channel region, and further comprising a bottom barrier layerdisposed between the substrate and the three-dimensional group III-Vmaterial body; a source and drain material region disposed above thethree-dimensional group III-V material body; a trench disposed in thesource and drain material region separating a source region from a drainregion, the trench also partially disposed in the bottom barrier layerand completely exposing the channel region; and a gate stack disposed inthe trench and on and completely surrounding the channel region, thegate stack comprising: a first dielectric layer conformal with thetrench and disposed on the exposed portion of the channel region; asecond, different, dielectric layer conformal with and disposed on thefirst dielectric layer, but not on the channel region; and a gateelectrode disposed on the second dielectric layer.
 17. The semiconductordevice of claim 16, wherein the second dielectric layer has a higherdielectric constant than the first dielectric layer.
 18. Thesemiconductor device of claim 17, wherein the second dielectric layerhas a dielectric constant greater than approximately 8 and the firstdielectric layer has a dielectric constant approximately in the range of4-8.
 19. The semiconductor device of claim 17, wherein the seconddielectric layer comprises a material selected from the group consistingof tantalum silicon oxide (TaSiO_(x)), aluminum oxide (AlO_(x)), hafniumoxide (HfO₂), zirconium oxide (ZrO₂), and lanthanum oxide (La₂O₃), andthe first dielectric layer comprises a material selected from the groupconsisting of aluminum silicate (AlSiO_(x)), silicon oxynitride (SiON),silicon dioxide (SiO₂) and silicon nitride (Si₃N₄).
 20. Thesemiconductor structure of claim 16, wherein the first dielectric layerhas a thickness approximately in the range of 0.3-2 nanometers, and thesecond dielectric layer has a thickness approximately in the range of0.5-3 nanometers.
 21. The semiconductor structure of claim 16, thehetero-structure further comprising: a top barrier layer disposedbetween the source and drain material region and the three-dimensionalgroup III-V material body, wherein the trench is also disposed in thetop barrier layer. 22-23. (canceled)
 24. A semiconductor device,comprising: a vertical arrangement of a plurality of group III-Vmaterial nanowires disposed above a substrate; a gate stack disposed onand completely surrounding channel regions of each of the group III-Vmaterial nanowires, the gate stack comprising: a first dielectric layerdisposed on each of the channel regions; a second, different, dielectriclayer conformal with the first dielectric layer and disposed on thefirst dielectric layer, but not on each of the channel regions; and agate electrode disposed on the second dielectric layer; and source anddrain regions surrounding portions of each of the group III-V materialnanowires, on either side of the gate stack.
 25. The semiconductorstructure of claim 24, further comprising: a top barrier layer disposedbetween the source and drain regions and each of the group III-Vmaterial nanowires.
 26. The semiconductor structure of claim 24, furthercomprising: a bottom barrier layer disposed between the substrate andthe bottom-most group III-V material nanowire, wherein a bottom portionof the gate stack is disposed on the bottom barrier layer.
 27. Thesemiconductor device of claim 24, wherein the second dielectric layerhas a higher dielectric constant than the first dielectric layer. 28.The semiconductor device of claim 27, wherein the second dielectriclayer has a dielectric constant greater than approximately 8 and thefirst dielectric layer has a dielectric constant approximately in therange of 4-8.
 29. The semiconductor device of claim 27, wherein thesecond dielectric layer comprises a material selected from the groupconsisting of tantalum silicon oxide (TaSiO_(x)), aluminum oxide(AlO_(x)), hafnium oxide (HfO₂), zirconium oxide (ZrO₂), and lanthanumoxide (La₂O₃), and the first dielectric layer comprises a materialselected from the group consisting of aluminum silicate (AlSiO_(x)),silicon oxynitride (SiON), silicon dioxide (SiO₂) and silicon nitride(Si₃N₄).
 30. The semiconductor structure of claim 24, wherein the firstdielectric layer has a thickness approximately in the range of 0.3-2nanometers, and the second dielectric layer has a thicknessapproximately in the range of 0.5-3 nanometers.
 31. A semiconductordevice, comprising: a vertical arrangement of a plurality of group III-Vmaterial nanowires disposed above a substrate; a gate stack disposed onand completely surrounding channel regions of each of the group III-Vmaterial nanowires, the gate stack comprising: a first dielectric layerdisposed on outer portions, but not an inner portion, of each of thechannel regions; a second, different, dielectric layer conformal withthe first dielectric layer and disposed on the inner portion of each ofthe channel regions; and a gate electrode disposed on the seconddielectric layer; source and drain regions surrounding portions of eachof the group III-V material nanowires, on either side of the gate stack;and a top barrier layer disposed between the source and drain regionsand each of the group III-V material nanowires.
 32. The semiconductordevice of claim 31, wherein the second dielectric layer has a higherdielectric constant than the first dielectric layer.
 33. A semiconductordevice, comprising: a hetero-structure disposed above a substrate andcomprising a three-dimensional group III-V material body with a channelregion; a source and drain material region disposed above thethree-dimensional group III-V material body; a trench disposed in thesource and drain material region separating a source region from a drainregion, and exposing at least a portion of the channel region; and agate stack disposed in the trench and on the exposed portion of thechannel region, the gate stack comprising: a first dielectric layerconformal with the trench and disposed on the exposed portion of thechannel region; a second, different, dielectric layer conformal with anddisposed on the first dielectric layer, but not on the channel region,wherein the second dielectric layer has a dielectric constant greaterthan approximately 8 and the first dielectric layer has a dielectricconstant approximately in the range of 4-8; and a gate electrodedisposed on the second dielectric layer.
 34. The semiconductor structureof claim 33, wherein the first dielectric layer has a thicknessapproximately in the range of 0.3-2 nanometers, and the seconddielectric layer has a thickness approximately in the range of 0.5-3nanometers.
 35. A semiconductor device, comprising: a hetero-structuredisposed above a substrate and comprising a three-dimensional groupIII-V material body with a channel region; a source and drain materialregion disposed above the three-dimensional group III-V material body; atrench disposed in the source and drain material region separating asource region from a drain region, and exposing at least a portion ofthe channel region; and a gate stack disposed in the trench and on theexposed portion of the channel region, the gate stack comprising: afirst dielectric layer conformal with the trench and disposed on theexposed portion of the channel region; a second, different, dielectriclayer conformal with and disposed on the first dielectric layer, but noton the channel region, wherein the second dielectric layer has a higherdielectric constant than the first dielectric layer, and wherein thesecond dielectric layer comprises a material selected from the groupconsisting of tantalum silicon oxide (TaSiO_(x)), aluminum oxide(AlO_(x)), hafnium oxide (HfO₂), zirconium oxide (ZrO₂), and lanthanumoxide (La₂O₃), and the first dielectric layer comprises a materialselected from the group consisting of aluminum silicate (AlSiO_(x)),silicon oxynitride (SiON), silicon dioxide (SiO₂) and silicon nitride(Si₃N₄); and a gate electrode disposed on the second dielectric layer.36. The semiconductor structure of claim 35, wherein the firstdielectric layer has a thickness approximately in the range of 0.3-2nanometers, and the second dielectric layer has a thicknessapproximately in the range of 0.5-3 nanometers.